1. Field of the Invention
The present invention relates to a cylindrical grinding method and a cylindrical grinding machine.
2. Description of Related Art
Japanese Patent Application Publication No. 2011-104675 describes a method for grinding a cylindrical workpiece. In this grinding method, rough grinding is first performed, precision grinding as a finish grinding step is subsequently performed after the diameter of the workpiece reaches D1, and fine grinding as another finish grinding step is performed after the diameter of the workpiece reaches D2. The timing for switching from the rough grinding to the precision grinding and the timing for switching from the precision grinding to the fine grinding are determined based on measurement values obtained by a sizing device for measuring the outer diameter of the workpiece.
The rough grinding is performed at a high grinding efficiency, and therefore generates a shape deviation from a perfect round shape. The workpiece is, however, ground in the finish grinding step as a post-process so as to reduce the amount of shape deviation from a perfect round shape to a value within a predetermined range. The timing for switching from the rough grinding to the finish grinding is set so as to reduce the amount of shape deviation to a value within a predetermined range. The diameter of the workpiece corresponding to the timing for switching from the rough grinding to the finish grinding is set in advance.
The grinding wheel is subjected to truing at appropriate times because the grinding wheel changes in grinding performance and clogging state. Therefore, the diameter of the workpiece at which the finish grinding is to start is set taking into account the change in the grinding performance and the change in the clogging state of the grinding wheel.
For example, the grinding wheel has good grinding performance and has almost no clogging immediately after the truing. Therefore, immediately after the truing, the shape deviation can be eliminated in a relatively short time since the switching to the finish grinding. After many workpieces are ground since the truing of the grinding wheel, the grinding performance of the grinding wheel degrades, and the grinding wheel is clogged. Therefore, in the state after many workpieces are ground since the truing of the grinding wheel, the shape deviation can be eliminated after a relatively long time has elapsed since the switching to the finish grinding.
As described above, the diameter of the workpiece corresponding to the timing for switching from the rough grinding to the finish grinding is a value set in advance, and hence is set to a value with which the shape deviation can be eliminated in the state after many workpieces are ground since the truing of the grinding wheel. Due to this, depending on circumstances, cases occur where the finish grinding is performed for an unnecessarily long time.